It is important in this practical activity to safely use a Bunsen burner and a water bath. This includes the safe use of a range of equipment to separate and purify mixtures, including filtration and crystallisation.
This outlines one way to carry out the practical using copper(II) oxide powder and dilute sulfuric acid. Eye protection must be worn.
To investigate the preparation of pure, dry hydrated copper(II) sulfate crystals starting from copper(II) oxide.
1. Add some dilute sulfuric acid to a small beaker.
2. Add some hot water from a kettle to larger beaker. Place the beaker of sulfuric acid into the hot water to warm up the acid.
3. Add a spatula of copper(II) oxide powder to the acid and stir with a glass rod. Continue adding copper(II) oxide powder until it is in excess and remains as a black powder in the solution.
4. Fold a piece of filter paper and put it into a filter funnel. Fit the filter funnel into a conical flask.
5. Add the reaction mixture from the beaker to the filter paper.
6. Collect the filtrate, which is the copper(II) sulfate solution. Dispose of the residue, which is the unreacted copper(II) oxide.
7. Pour the filtrate into an evaporating basin.
8. Set up a Bunsen burner, tripod and gauze on a heat resistant mat.
9. Put a beaker of water on the gauze and the evaporating basin on the beaker.
10. Heat the water, adjusting the Bunsen burner flame so the water is just simmering.
11. Stop heating before all the water in the evaporating basin leaves the copper(II) sulfate solution.
12. Allow the evaporating basin to cool, then leave it aside for a few days.
Record the appearance of the copper(II) sulfate crystals, including their colour and shape.
Hydrated copper(II) sulfate crystals should be blue and regularly shaped. Describe how your crystals compare to this description. Suggest an explanation for any differences.
Explain why the sulfuric acid is warmed at step 2.
Warm acid will react faster than cold acid, helping to ensure that all the acid reacts with the copper(II) oxide.
Evaluate the hazards and the precautions needed to reduce the risk of harm. For example:
|Hazard||Possible harm||Possible precaution|
|Sulfuric acid||Concentrated acid is corrosive and damages skin and clothes||Use dilute sulfuric acid|
|Boiling water bath||Skin burns||Ensure the boiling water bath is stable on the gauze|
|Hot copper(II) sulfate solution spitting out during crystallisation||Damage to eyes and skin||Wear eye protection and avoid standing over the hot apparatus|